1. Field of the Invention
This invention relates to a swing-arm type linear d.c. brushless motor (hereinafter called "swing-arm type linear motor") suitable for use in a rotating magnetic positioner mechanism, which is useful for feeding a magnetic head of a magnetic disk unit having a relatively small capacity, or the like.
2 Description of the Related Art
A demand for high-density recording of information has resulted in frequent use of magnetic disk units. These magnetic disk units use a magnetic head for conducting read and write transfer of information from and into a disk are equipped with a magnetic head positioner mechanism for moving the magnetic head to a predetermined position.
Magnetic head positioner mechanisms include both linear and rotating types. The former is suitable for use in large-capacity magnetic disks, and the latter is suitable for use in a small-and medium-capacity magnetic disks.
A recent demand for small and/or portable units has resulted in a need for smaller, lower capacity and economical magnetic disk units. Also, magnetic head positioner mechanisms suitable therefor have been required.
In conventional magnetic head positioner mechanisms, the following means are used to permit the control of the feed ratio and position of a magnetic head. One of plural magnetic disks is sacrificed to contain positional information (such a magnetic disk is so-called a "positional information disk") so as to control the feed ratio and position of the magnetic head by information detected by the magnetic head and feeding it back to a control system.
However, the recent demand for small and/or portable units, has been met by small-size, small-capacity and economical magnetic disk units such as those using only one magnetic disk and those having no positional information disk even when plural magnetic disks have been used.
Here, since a magnetic disk unit having no postional information disk can not detect the feed ratio and position of its magnetic head, it must be provided with some other means for this purpose.
For such a detecting means, it has been known to use a linear potentiometer from which linear electric signals are output. However, it requires an A/D converter and hence has drawbacks in that it becomes complicated, large, and is costly.
Although there is a method arranging encoder as another method, it is necessary to use a highly precise, large-size and expensive encorder in order to detect the microfeed and position of the magnetic head. It is hence difficult to provide a small-size, small-capacity and economical magnetic disk unit.